1. Field of the Invention
The present invention relates to the field of audiometric testing.
2. Description of the Related Art
Audiometer systems are used to test hearing of people referred to as test subjects. In general, an audiometer provides electrical signals to earphones. The earphones are placed one of over and in the ears of the test subject. The earphones convert the electrical signals to audible test sounds at the ears of the test subject. The test subject typically raises a hand or finger in response to detecting a test sound.
Prior art audiometer systems use wire tethers to connect the audiometer to the earphones. A bone conduction transducer may be used in addition to the earphones. In the art, the bone conduction transducer may also be referred to as an oscillator or a vibrator. The audiometer system may also have a user response button as an indicator to the examiner of the test subject's detection of the test sounds. Where recorded or live speech is used as test material, a response from the test subject will generally be verbal. The response will typically be communicated to the examiner via a microphone positioned inside an audiometric test booth.
The wire tethers are a weak and bothersome link. Approximately 80% of audiometer system failures result from failures of the wire tethers. When the wire tethers fail, costs accrue from repair bills and downtime. The wire tethers add to space requirements in portable audiometer systems. Additionally, the wire tethers add to the time and inconvenience associated with setting up and dismantling the portable audiometer systems. The wire tethers confine the test subject to a chair within the audiometric test booth. Confinement to the chair may severely limit testing with young children who may have limited or no tolerance for that restriction.
Design improvements to wire tethered systems have included evaluation of wireless links. Audiometer systems with the wireless link must provide the same sound signals with the same accuracy as the audiometer systems with the wire tether. For example, the audiometer systems must produce signals in a very wide dynamic range. A clinical audiometer must produce sounds in the range −10 dBHL to 110 dBHL (wherein HL refers to Hearing Level). Audiometers must comply with US and international standards including ANSI S3.6-2004, “Specification for Audiometers” and ISO 389-2 “Acoustics—Reference zero for the calibration of audiometric equipment—Part 2: Reference equivalent threshold sound pressure levels for pure tones and insert earphone.” Test environments must comply with ANSI S3.1-1999 “Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms.” These standards include requirements for high signal to noise ratio, low harmonic distortion, and high adjacent channel rejection.
Early attempts at using the wireless link were based on analog FM radio technology. However, the analog FM radio technology cannot transmit the wide dynamic range required from the clinical audiometer. A high quality FM transmitter cannot transmit a linear signal with more than approximately 70 dB of dynamic range. It is also known that in order to transmit a wider dynamic range, the analog FM transmitter must incorporate an analog COMPANDER (non-linear audio processing that compresses a signal at the input to a transmitter and expands the signal at the output from a receiver). In the field of audiometric testing it is unacceptable to apply non-linear processing to the electrical signals transmitted (also referred to as test signals) to the earphones. Furthermore, accurate audiometric testing requires very stable conditions without interferences and fluctuations of the test signals. Analog FM radio systems are susceptible to radio signal interferences. Additionally, noise levels of the analog FM radio signals are subject to reception conditions. Another known problem of the analog FM transmitters is poor channel rejection in cases when two or more channels (i.e., stereo) are multiplexed on a same radio carrier signal.
U.S. Pat. No. 4,964,304, dated Oct. 23, 1990, entitled “AUDIOMETRIC TESTING METHOD AND APPARATUS,” discloses “Means for transmitting an FM radio signal carrying an audio test signal to a preselected one of two receivers in the headset of a patient, together with FM signalling means carried by the patient to transmit signals to the audiometer indicating which of the patient's ears received the test signal to permit the patient to have virtually unlimited mobility during the testing procedure. Separate FM signal channels may be provided to permit simultaneous testing of a plurality of patients. Furthermore, if desired, a predetermined pattern of test signals may be recorded and means may be provided for automatically transmitting the test signals and recording the patient response signals, thereby permitting fully automatic testing to be conducted.”
What are needed are methods and apparatus for providing more reliable and convenient electrical signal connections in audiometer systems.